Calcium is much more important for plant growth than people think. Plants need more calcium than phosphorus, and a calcium deficiency can create a cascade of problems that are often difficult to diagnose. Calcium-deficient plants show the worst symptoms of any nutrient deficiency, often showing signs of multiple nutrient deficiencies.
Calcium strengthens cell walls. Therefore, when cells weaken, the plant's vascular system begins to collapse, reducing the uptake of all major elements. Symptoms occur first at the apex of growth of both shoots and roots. Calcium is an immobile element, which means that if there is a deficiency, the plant cannot translocate calcium from older to younger leaves. New growth on the tips and edges of leaves begins to wilt and die, and new leaves are often deformed.
Calcium, the forgotten nutrient
But the most serious effect of calcium deficiency occurs in the roots. Calcium is involved in root extension and is necessary for the secretion of protective mucilage around the roots. Calcium deficiency also increases the plant's susceptibility to root diseases, such as Pythium. Without sufficient calcium, roots often become stunted and discoloured and begin to lose solutes that plants need to grow. This results in a thin, peeling root system that often becomes slimy, brown, or black, especially at the apex of the roots. If plants do not have actively growing roots, other nutrient deficiencies may appear, often randomly.
The first step to prevent calcium deficiency is to use a source of water-soluble calcium by foliar application, but this may not increase the amount of calcium in the plants, as rapid growth will dilute the amount of calcium applied. Keep in mind that some calcium sources are poorly soluble and are released only very slowly over time; in addition, calcium quickly locks in with phosphates and sulphates, forming insoluble precipitates. In our experience, the best way to apply calcium effectively is to use granular forms of gypsum.
Adding gypsum to the soil can significantly increase the rate of irrigation water infiltration under three conditions:
Because gypsum – calcium sulfate – is a neutral salt it affects soil pH very slowly, causing it to seek neutral soil pH (7.0) over time. It won’t break up hard pans or soil layers with distinctly different soil textures or reduce compaction that impedes water infiltration. Instead, gypsum stabilizes the soil, reducing dispersion of larger soil aggregates when a dry soil is irrigated. In turn, this reduces the formation of soil crusts, opening the soil and allowing more water to soak in rather than run off.
So, why is June an ideal time for growers using flood or wide-coverage sprinklers to apply gypsum on the soil surface for improving irrigation water infiltration? Because that’s when soil infiltration rates tend to decline, temperatures are rising, and plants start using more water.
A second application in late autumn will encourage roots growth and strengthen the plants cells against frost. The storage of carbohydrates in the roots will promote the beneficial cooperation with soil biology that will remain active mining other nutrients from the soil and make them available for the next spring.
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